Looking at my recent plot, I think a 4-2-1 will be the way to go.

I currently have 1.75" primaries, the calculations off the design equations show these to be on the larger side, my silencer is 3".

Would it be fine to make the secondary's the same diameter? Any advice?

Thanks

Quick recalc, I'm thinking:

26" overall primary length
1.75" primary diameter
2" secondary diameter
Into a 3" silencer

Will see how it goes.